• Metal work is back.

    Marcus • 4 days ago • 0 comments

    When I got the call to say the metal work was ready to be welded I took the chance to help out (I just stood back and watched).

    Because I went for tab and slot construction it was a pretty quick process to assemble and weld with lots of attention paid to making sure that the parts were square but not necessarily dimensionally accurate.  All of the weather covers would eventually be 3D printed so I could amend the designs to account for any errors induced during welding. 

    With all the parts welded up I loaded the car and took them home to begin test fitting,

    The original plan had been to add in a few additional holes that I missed in the initial design such as the AZ home sensor (photos below) and ensure that everything would fit prior to sending it away for powder coat. Spoiler alert, I never account for the welds and they got in the way of the AZ stepper motor.

    But....... it got the better of me and I ended up fitting all of the parts I had on hand and wired up a dodgy controller so that I could get some motion working.

  • Parts start to arrive.

    Marcus • 6 days ago • 0 comments

    With my steppers motors on order it was time to start thinking about bearings and slip rings. I knew that I wanted the ability to have continuous rotation which meant slip rings. Trying to find a bearing that had a decent shaft diameter but wasn't designed for a large rotary turntable was impossible. So in what at this point was becoming a theme for this build.... I brought a monster bearing. 

    It's greasable, mounted with 8 x M8 bolts and is insane overkill. But it gives me lots of room for a centrally mounted slip ring and I know that no matter how unbalanced the load ever gets that this bearing isn't going to be the thing to fail.

    About the same time that the bearing arrived my first motor turned up. Sitting them side by side on my bench I realised that I may have overdone it and starting questioning just how much power this thing would have but also how much it was going to weigh. So in typical fashion I started to design the mount to be made from 5mm steel. I decided on a tab and slot style construction instead of trying to factor in material loss due to bends etc. 

    I came up with three main assemblies to be welded together out of lots of little parts. There was the base which doubled as the AZ section, the ALT section and the equipment shelf which was designed to hold a Losmandy clamp, spotting camera and laser pointer.

    And off the designs went to my metal fab shop.

  • What specs and my first orders...

    Marcus • 6 days ago • 0 comments

     After the initial excitement of researching mounts and optical tubes and all things telescopes I decided that I should just buy something off the shelf.....

    That lasted for about five minutes before I started researching specs and working out what it would take to build something. I spent a little time contemplating between and ALT/AZ or a EQ mount but given that I wanted to use the mount for ground based targets as well as astronomical I pretty quickly decided on ALT/AZ.

    The speeds and accuracy of something like the Planewave I-350 seemed to be a good target and I started doing the maths to see what combination of gears, belts and motors would give me good tracking speeds whilst also allowing small enough step sizes that I could try my hand at some long exposure astronomical photography.

    I decided to buy the biggest stepper motors I could reliably fit into a mount and then microstep them as far as possible to get the minimum step size down. My final drive train would look something like a Nema 34 motor @ 12nm with microstepping set @ 40,000 steps per rotation. I based my calculations on a 30t gear on the stepper and a 160t gear on the output for a minimum step size of 0.0016875° or 6.075 arcseconds.

    The Planewave has a minimum step size of roughly 0.07 arcseconds, so I'm along way off that but I can still add in a reduction gearbox if needed. I double checked a few other numbers such as expected RPM and with control signals at 200 kHz I could expect 56 RPM on the final stage which was more than quick enough.

    So in went the order for two closed loop Nema 34 kits to start basing the build on.